Ducts and conduits are used to convey air in building heating, ventilation and air conditioning (HVAC) systems. In many applications, especially in commercial and industrial constructions, the ducts are lined with flexible thermal and acoustic insulating material. The lining enhances the thermal efficiency of the duct work and reduces noise associated with movement of air therethrough. Duct liners may comprise any suitable organic material or inorganic material, e.g., mineral fibers such as fiber glass insulation or the like. Typical fiber glass duct liners, for example, are constructed as fiber glass mats having densities of about 1.5 to 3 pounds per cubic foot (pcf) and thicknesses of about 0.5 to 2 inches.
To prevent fiber erosion due to air flow, the insulation may include a coating or a facing layer on its inner or “air stream” surface. The air stream surface of the insulation is the surface that conveys air through the duct and is opposite the surface that contacts the duct sheet metal in the final duct assembly. Examples of such duct liners are provided in U.S. Pat. Nos. 3,861,425 and 4,101,700. Several insulation duct liners are marketed under the trade designations TOUGHGARD® duct liner by CertainTeed Corp. of Valley Forge, Pa., AEROFLEX® and AEROMAT® duct liner by Owens Corning Fiberglass Corp. of Toledo, Ohio, PERMACOTE®, and POLYCOUSTIC™ duct liner by Johns Manville Corp. of Denver, Colo.
As an alternative to coated duct liners, manufacturers such as CertainTeed Corp. and Knauf Fiber Glass GmbH offer duct liners having glass fiber insulation covered with a layer of non-woven facing material which defines the air stream surface of those products. The facing material produces a durable surface that protects the air duct from fiber erosion.
In traditional duct liners, phenolic powder resin binders are used to bond the fibers together. These resin binders, such as phenol-formaldehyde, generally contain formaldehyde. Although there is no health risk with the traditional fiber glass duct liners using formaldehyde-containing binders, formaldehyde at higher levels may cause skin irritation and sensitivity. In consideration of such concerns, manufacturers of insulation products have started to offer formaldehyde-free products to provide the consumers an alternative to the traditional insulation products including duct liners.
These currently existing formaldehyde-free insulation products use water soluble acrylic binders that are formaldehyde-free in place of the phenolic powder resin binders. Some examples of formaldehyde-free binders used in such applications can be found in U.S. Pat. Nos. 5,932,665 and 6,331,350. However, because these acrylic binders are applied in aqueous form, they are generally more difficult to use in manufacturing process compared to binders in dry form. Thus, there is a need for formaldehyde-free duct liners fabricated with dry formaldehyde-free binders without compromising on the manufacturability and the performance characteristics of the duct liners.
It is also recognized that there is a need for a continuous process for forming duct liner by the air laid manufacturing method. For various reasons, such as limitations on manufacturing space, the process of making a faced duct liner is not continuous with the process of coating the duct liner with a water resistant layer. In the prior art process, after the duct liner is formed with a facing layer on the air stream surface thereof, the duct liner is then cut to length and rolled for temporary storage. The roll is later moved to a separate coating system, where it is unwound, coated and then rolled and packaged. The transfer of the basic mats from the production line to the coating line is a manual process that results in low product efficiency and increased labor demands.